280 OSTEOLOGY. 



upper limb reacting on the form of the bone of that side. The influence of muscular action, 

 however, does not wholly account for the production of the curves of the bone, since the bone 

 has been shown to display its characteristic features in cases where there has been defective de- 

 velopment or absence of the upper limb (Reynault). Partial or complete absence of the clavicle 

 has been recorded. W. S. Taylor exhibited an interesting case of this kind at the Clinical 

 Society of London, October 25, 1901. Sometimes there is a small canal through the anterior 

 border of the bone near its middle for the transmission of one of the supra-clavicular nerves. 



Scapula. The most common variation met with is a separated acromion. In these 

 cases there has been failure in the ossific union between the spine and acromion, the 

 junction between the two being effected by a layer of cartilage or by an articulation possessing a 

 joint cavity. The condition is usually symmetrical on both sides, though instances are recorded 

 where this arrangement is unilateral. Very much rarer is the condition in which the coracoid 

 process is separable from the rest of the bone. The size and form of the scapular notch differs. 

 In certain cases the superior border of the bone describes a uniform curve reaching the base 

 of the coracoid without any indication of a notch. In some scapulae, more particularly in 

 those of very old people, the floor of the subscapular fossa is deficient owing to the absorption of 

 the thin bone, the periosteal layers alone filling up the gap. 



At birth the vertical length of the bone is less in proportion to its width than in the adult. 



Humerus. As has been stated in the description of the bone, the olecranon and coro- 

 noid fossae may communicate with each other in the macerated bone. The resulting supra- 

 trochlear foramen is most commonly met with in the lower races of man, as well as in the 

 anthropoid apes, and in some other mammals. The occurrence of a hook -like spine, called the 

 epicondylic process, which projects in front of the medial epicondylic ridge, is not uncommon. 

 Its extremity is connected with the medial epicondyle by means of a fibrous band, underneath 

 which the median nerve, accompanied by the brachial artery, or one of its large branches, may 

 pass, or in some instances, the nerve alone, or the artery unaccompanied by the nerve. This 

 arrangement is the homologue in a rudimentary form of a canal present in many animals, 

 notably in the carnivora and marsupials. In addition to the broad radial groove already 

 described, and which is no doubt produced by the twisting or torsion of the body, there is 

 occasionally a distinct narrow groove posterior to it, which marks precisely the course of the 

 radial nerve as it turns round the lateral side of the body of the bone. 



Ulna. Cases of partial or complete absence of the ulna through congenital defect have 

 been recorded. Rosenm tiller has described a case in which the olecranon was separated from the 

 proximal end of the bone, resembling thus in some respects the patella. In powerfully developed 

 bones there is a tendency to the formation of a sharp projecting crest corresponding to the inser- 

 tion of the triceps. 



Radius. Cases of congenital absence of the radius are recorded; in these the thumb is 

 not infrequently wanting as well 



Carpus. Increase in the number of the carpal elements is occasionally met with, and 

 these have been ascribed to division of the navicular, os lunatum, os triquetrum, capitate, lesser 

 multangular, and os hamatum. Of these the most interesting is the OS centrale, first described 

 by Rosenberg, and subsequently investigated by Henke, Leboucq, and others. This is met with 

 almost invariably as an independent cartilaginous element during the earlier months of fcetal 

 life, and occasionally becomes developed into a distinct ossicle placed on the back of the carpus 

 between the navicular and capitate bones and the lesser multangular. Its significance depends 

 on the fact that it is an important component of the carpus in most mammals, and is met 

 with normally in the orang and most monkeys. Ordinarily in man, as was pointed out by 

 Leboucq, it becomes fused with the navicular, where its presence is often indicated by a small 

 tubercle, a condition which obtains in the chimpanzee, the gorilla, and the gibbons. Dwight 

 has described a case in which there was an os subcapitulum in both hands. The ossicle lay 

 between the base of the middle metacarpal bone and the capitate bone, with the lesser multangular 

 to its radial side. (Anat. Anz. vol. xxiv.) Further addition to the number of the carpal elements 

 may be due to the separation of the styloid process of the third metacarpal bone and its persistence 

 as a separate ossicle. 



Reduction in the number of the carpus has been met with, but this is probably due to 

 pathological causes. Morestin (Bull Soc. Anat. de Paris, tome 71, p. 651), who has investigated 

 the subject, finds that ankylosis occurs most frequently between the bases of the second and 

 third metacarpal bones and the carpus, seldom or never between the carpus and the first meta- 

 carpal, or between the pisiform and os triquetrum. Instances of complete fusion of the os 

 lunatum and triquetral bones, without any apparent pathological change, have been recorded 

 in Europeans, Negroes, and an Australian. 



Metacarpal Bones. As previously stated above, the styloid process of the third 

 metacarpal bone appears as a separate ossicle in about 1/8 per cent, of cases examined. (" Fourth 

 Annual Report of the Committee of Collect. Invest. Anat. Soc. Gt. Brit, and Ireland," Journ. 

 Anat. and Physiol. vol. xxviii. p. 64) In place of being united to the third metacarpal, 

 the styloid process may be fused with either the capitate bone or the lesser multangular, under 

 which conditions the base of the third metacarpal bone is without this characteristic apophysis. 



Phalanges. Several instances have been recorded of cases in which there were three phalanges 

 in the thumb. Bifurcation of the terminal phalanges has occasionally been met with, and examples 

 of suppression of a phalangeal segment or its absorption by another phalanx have also been de- 

 scribed. (Hasselwander, Zeits. fur Morph. u. Anthr. vol. vi. 1903.) 



